1. Field of the Invention
The present invention relates to a phase calibration circuit, and more particularly, to a phase calibration circuit and related phase calibration method applied in a receiver of a communication system.
2. Description of the Prior Art
In a pass-band communication system, a baseband signal is modulated onto a carrier and becomes a modulated signal, and a transmitter transmits the modulated signal to a receiver via a channel. Then, for the convenience of the following signal processing, the receiver demodulates the modulated signal to remove the carrier component or decrease a frequency of the carrier. However, generally, the carriers of the transmitter and the receiver are not synchronous, and therefore carrier frequency offset and carrier phase offset issues exist. Therefore, the receiver generally includes a carrier recovery circuit to overcome these issues.
A general carrier recovery circuit includes a signal processing module, a phase calibration module, a phase detector, a filter and a carrier phase accumulator, where a position of the phase calibration module can be determined according to the designer's consideration, that is, the phase calibration module can be positioned before or after the signal processing module. However, if the phase calibration module is positioned before the signal processing module (that is the phase calibration module is used to calibrate an input signal of the signal processing module), the carrier recovery circuit cannot accurately calibrate the carrier phase of the input signal due to a phase difference between a feedback signal and the input signal, and therefore suffers a “tracking” issue. In addition, if the phase calibration module is positioned after the signal processing module, although there is no “tracking” issue, the carrier phase deviation of the signal processed by the signal processing module still exists. Therefore, the designs of the signal processing module are more complex due to the considerations of the carrier phase deviation effect.